基础 (jī chǔ) is a noun meaning 'foundation, basis' — the underlying support for ideas, systems, or learning. It differs from 基本 (jīběn, 'basic', an adjective) and 根本 (gēnběn, 'fundamental', often used in '根本原因'). Unlike 根据 (gēnjù, 'according to' / 'basis'), which is often a preposition, 基础 is used as a concrete or abstract noun.